This invention is generally directed to toner and developer compositions as well as the use of such compositions in various imaging systems. More specifically, the present invention is directed to toner materials containing interpenetrating polymer networks comprised of uncrosslinked polymers, incorporated into a polymer network of highly crosslinked polymers, and developer compositions containing such polymers. Toners containing such polymers have several improved characteristics, over many prior art toners including reduced gloss, improved blocking performance, superior offsetting characteristics, improved release properties, and the like. Accordingly, such toner compositions depending on the selection of the crosslinked and uncrosslinked polymers are useful in numerous types of imaging systems, including hot roll pressure fusing systems, cold pressure fusing systems, and the like, as more specifically detailed hereinafter.
The electrostatographic process, and more specifically the xerographic process is well known as documented in several prior art references. In these processes, an electrostatic latent image is developed by applying toner particles to the image, using for example cascade development magnetic brush development, or touchdown development. In some instances it may be desirable in such systems to produce a reverse copy of the original. Thus, for example, it may be desirable to produce a negative copy from a positive original, or a positive copy from a negative original, which is accomplished by modifying the triboelectric charging properties of the toner and carrier particles.
Toner particles utilized to develop latent images are usually present in a developing composition containing carrier particles, such as triboelectrically chargeable non-magnetic materials, or triboelectrically chargeable magnetic materials; the toner particles being electrostatically attractable to the carrier particles. The toner particles generally are comprised of a toner resin, and colorants or pigments such as carbon black. Subsequent to development, the image is transferred to a permanent substrate such as paper, and fixed thereto by a number of known methods including heat fusing, cold pressure fix fusing, and the like. Accordingly, the toner particles must possess properties so as to enable them to be properly fused without causing deterioration thereof, and thus adversely affecting the quality of the resulting images. Also, toner compositions that might be useful in heat fusing systems, are generally not useful with cold pressure fixing devices.
Furthermore, many of the prior art toner compositions utilized for developing electrostatic latent images transfer from the developed toner image present on the permanent substrate to the surface of the fusing members, particularly the heated fusing members. Such an undesirable transfer of toner particles not only disrupts the quality of subsequent images, but also contaminates the surface of the fusing member, causing the contaminated toner particles to be transferred to succeeding substrates or copying sheets when the fusing member is used in subsequent imaging cycles. In such instances, undesirable deposits of toner material are then formed in background areas, resulting in copies of low quality.
There is described in U.S. Pat. Nos. 4,217,406 and 3,938,992 crosslinked toner resins which are stated as overcoming some of the prior art problems associated with previous toner resins. For example, in U.S. Pat. No. 3,938,992 there is described improved developing compositions containing finely divided carrier particles, and finely divided crosslinked toner particles containing a fusible binder polymer, with the molecular chains of said binder polymer being crosslinked to an extent sufficient to extend the useful fusing range of the crosslinked toner particles by at least 10.degree. C., relative to comparable uncrosslinked toner particles comprising an identical binder polymer, with the exception that the molecular chains thereof are uncrosslinked, as are conventional toner binder polymers. More specifically, it is stated in this patent that the preferred styrene containing binder polymers are crosslinked to an extent sufficient to provide a useful fusing range of at least about 90.degree. C., and to extend the useful fusing range of the toner particles by at least about 20.degree. C. relative to comparable uncrosslinked toner particles comprising the same styrene containing polymer, except in an uncrosslinked form. Developing compositions containing such toners according to the teachings of this patent apparently substantially eliminate the transfer of undesirable toner particles to the fusing member referred to therein as "off-setting."
According to the disclosure of the '992 patent, the toner composition involved distinguishes over the toner composition described in U.S. Pat. No.3,804,764, in that the '764 toner is concerned primarily with the use of weakly crosslinked toners to provide a pressure fixable toner. In contrast, the crosslinked resins of the '992 patent contain linkages of sufficient strength so as to retain the crosslinks, thus, the crosslinks are not disrupted nor broken during fixing. Thus, it is the presence of these crosslinks in the toner polymer which during fixing provides the desired increase in useful fusing range. In the '764 patent, there is disclosed polymers that have weak crosslinks, which when used in an imaging system convert to an uncrosslinked state and then revert back to a weakly crosslinked state. Useful fusing range is defined in this patent as the difference in temperature between the minimum adequate fusing temperature and hot offset temperature. It is important to note that these patents teach the use of resins containing very low levels of crosslinking and further only a single main polymer and a crosslinking agent are employed. Additionally, there is no teaching in these patents as to the utilization of such toner resins in a number of different imaging systems, including hot roll fixing systems and cold pressure roll fusing devices, nor is there any teaching as to the employment of two polymers, one polymer contained in another polymer, one of which is highly crosslinked, the polymers being of different compositions.
Further, none of these patents disclose the cross-linking of one polymer in the presence of another polymer, as with the interpenetrating polymers of the present invention, nor do these patents disclose the importance of maintaining such polymers at the gel point or above. Thus, in the homogeneous systems described in the above-mentioned patents, partial crosslinking results in a very even or uniform structure, rather than, as in the present invention, the formation of small discontinuous domains of uncrosslinked polymer in a crosslinked polymer, similar to a sponge structure. Such a sponge-like toner composition imparts improved characteristics to toner compositions, enabling, for example, lower fusing temperatures, and superior fixing of the resulting image.
There thus continues to be a need for improved developing compositions, particularly improved oiless toner compositions which compositions can be used in a variety of different imaging devices, including devices employing hot roll fusing, cold pressure fixing, and the like. There also continues to be a need for improved toner compositions which are simple to reproduceably manufacture; and which compositions when used for developing images have improved offsetting characteristics, improved blocking performance, reduced gloss, and the like.